1. Field of the Invention
The present invention relates to a distance measuring apparatus installed in a camera and the like. In particular, the present invention relates to a distance measuring apparatus for precisely measuring a distance at infinity.
2. Description of Related Art
An auto-focus (which may be simply called “AF” hereinafter) method is a method for a generally used focus adjustment means in a camera. The AF method includes various methods such as an active method, a passive method, and a contrast method. For example, for a digital camera, AF by the contrast method is generally adopted. Since, the AF method by the contrast method uses image pickup signals, parallax does not occur, and a special sensor for AF is not required, which are big advantages.
Conventionally, a distance measuring apparatus by an external light passive method, which may be adopted for a compact camera, forms an image of a pencil of light of an object on a pair of line sensors through a pair of photoreceptive lenses. Then, the distance measuring apparatus detects a spacing between subject images on the pair of line sensor based on pixel outputs of the respective pair of line sensors, and calculates a distance to the object in accordance with the triangulation principle based on the base line length (that is, the spacing of the pair of photoreceptive lenses.
The distance measuring apparatus moves focus lenses of a shooting lens of a camera based on the distance. The line sensor may be an array of photoreceptors, such as CMOS line sensors and a CCD (charge Coupled Device) line sensor.
As shown in FIG. 19, a photoreceptive portion of a distance measuring apparatus by the external light passive method includes a pair of photoreceptive lenses L1 and L2 and a pair of line sensors S1 and S2. Ideally, a line BL connecting light axes of the pair of photoreceptive lenses L1 and L2 and a line Bs connecting the centers of the pair of line sensors S1 and S2 are parallel after the assembly. However, in reality, due to the errors caused in the assembly and/or variations in parts, the line BL connecting the lens light axes and the line Bs connecting the centers of the sensors are not parallel and have an angle θ therebetween, as shown in FIG. 19.
FIGS. 20A to 20F are diagrams each showing an image-forming position on a line sensor in accordance with a subject pattern. FIG. 20A is a diagram showing an ascending-toward-right diagonal pattern subject. FIG. 20B is a diagram showing a vertical pattern subject. FIG. 20C is a diagram showing an ascending-toward-left diagonal pattern subject. FIG. 20D is a diagram showing image-forming positions of the ascending-toward-right diagonal pattern subject on the line sensors S1 and S2. FIG. 20E is a diagram showing image-forming positions of the vertical pattern subject on the line sensors S1 and S2. FIG. 20F is a diagram showing an image-forming position of the ascending-toward-left diagonal pattern subject on the line sensors S1 and S2. Here, FIGS. 20D to 20F are diagrams each showing a case where the line BL connecting the light axes of the pair of photoreceptive lenses L1 and L2 is not parallel with the line Bs connecting the centers of the pair of line sensors S1 and S2 and a rotational error θ occurs therebetween, as shown in FIG. 19. D1 indicates a distance between images P1 and P2 upon the ascending-toward-right diagonal pattern subject distance measurement in FIG. 20D. D2 indicates a distance between the images P1 and P2 upon the vertical pattern subject distance measurement in FIG. 20E. D3 indicates a distance between the objects P1 and P2 upon the ascending-toward-left diagonal pattern subject distance measurement in FIG. 20F.
With the distance measuring apparatus having the lines BL and Bs at the angle θ as shown in FIG. 19, the distance D between the images P1 and P2 formed on the pair of line sensors S1 and S2 varies from line D1 to D3 (D1>D2>D3) shown in FIGS. 20D to 20F, which results in a distance measurement error. This is due to the angle (see FIGS. 20A to 20C) of the pattern P for the objects, even though the objects keep the same distance.
For example, when a landscape is shot as shown in FIG. 7A, which will be described later, the distance between the images P1 and P2 are large as shown in D1 in FIG. 20D because the ridgeline of the mountain has the ascending-toward-right diagonal pattern. Therefore, the measured distance data may shift to the closer distance side, and the infinity may not occur.
In order to solve these problems, a technology as disclosed in Japanese Unexamined Patent Application Publication No. 2000-206403 is known. In this case, a line sensor S3 is located at a position shifted by h in a direction perpendicular to the base line length direction toward one line sensor S2 of the pair of line sensors S1 and S2 as shown in FIG. 21. Then, an angle Ψ of a pattern P of the object is calculated from a distance X of the pattern P2 of the objects formed on the line sensors S2 and S3. Then, a distance D between the images P1 and P2 is corrected based on the angle Ψ and the angle θ (see FIG. 19) formed by the lines BL and Bs.
Furthermore, the applicant proposes, in Japanese Unexamined Patent Publication No. 3-64715, a technology relating to highly precise auto-focus camera effectively using an EEPROM on which various data can be written electrically.
The camera disclosed in Japanese Unexamined Patent Publication No. 3-64715 requires a dedicated checker, which is caused to communicate with a microcomputer so as to easily adjust correction data written in the EEPROM. Furthermore, the commonality of parts tends to be required for reducing the costs. When an electronic circuit including the microcomputer and the EEPROM is implemented on a printed circuit board, the mass production of the parts at one place can minimize the costs. In this case, the effect of the adoption of the checker may be large.